Methine dye compounds have been conventionally used as a spectral sensitizing dye for silver halide photographic light-sensitive materials. With respect to the technology for improving the light absorptivity of a silver halide grain, the following techniques are known. In order to improve the light absorptivity per one grain, the adsorption density of the sensitizing dye to a silver halide grain must be increased, however, a normal spectral sensitizing dye adsorbs as a monomolecular layer almost in the maximum density filling state and does not adsorb any more.
For the purpose of solving this problem, several proposals have been heretofore made. P. B. Gilman, Jr. et al., Photographic Science and Engineering, Vol. 20, No. 3, page 97 (1976) describes a technique of allowing a cationic dye to adsorb as a first layer and an anionic dye to adsorb as a second layer using electrostatic force. U.S. Pat. No. 3,622,316 (G. B. Bird et al.) describes a technique of allowing a plurality of dyes to adsorb in multiple layers to a silver halide grain and attaining the sensitization by virtue of Forster-type excited energy transfer.
JP-A-63-138341 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-64-84244 (both Sugimoto et al.) describe a technique of performing the spectral sensitization using the energy transfer from a light-emitting dye.
These techniques all have been proposed with an attempt to allow a dye to adsorb to a silver halide grain in excess of the saturated adsorption amount, however, the effect of elevating the sensitivity is not so high and there is a problem such as increase in the intrinsic desensitization.
On the other hand, U.S. Pat. Nos. 2,393,351, 2,425,772, 2,518,732, 2,521,944 and 2,592,196 and European Patent 565,083 describe a two components-connected dye in which two or more non-conjugated dye chromophores are connected through a covalent bond. This technique is, however, not intended to improve the light absorptivity. As for the technique of aggressively improving the light absorptivity, U.S. Pat. Nos. 3,622,317 and 3,976,493 (both G. B. Bird et al.) describe a technique of adsorbing a connection-type sensitizing dye molecule having a plurality of cyanine chromophores to increase the light absorptivity with an attempt to attain sensitization by the energy transfer, however, remarkable elevation of the sensitivity is not obtained.
JP-A-64-91134 (Ukai et al.) proposes a technique of connecting at least one substantially non-adsorptive dye containing at least two sulfo or carboxy groups to a spectral sensitizing dye capable of adsorbing onto silver halide.
Also, in the spectral sensitization, JP-A-6-27578 (Vishwakarma et al.) uses a 2 components-connected dye in which a cyanine dye adsorptive to silver halide and an oxonol not adsorptive to silver halide are connected, or EP-A-887700 (Parton et al.) uses a 2 components-connected dye in which an adsorptive cyanine dye and a non-adsorptive merocyanine dye or the like are connected using a specific linking group. In these techniques, however, the sensitivity is not sufficiently elevated by the energy transfer.
As such, sufficiently high elevation of the sensitivity is not yet achieved in any of these patents and publications and more development of techniques is being demanded.